The invention relates to a surface working broach for working the surfaces of forged cylindrical pins on workpieces, particularly for crankshafts, during rotation of the workpieces.
Customarily, crankpins as well as the major pins and the journal pins of cast or forged crankshafts are worked by rough turning or circular milling with subsequent finish turning and grinding. Roughing of the crankpins as produced by circular milling results in a polygonal surface configuration. To produce a round surface in the individual regions of the pin already at the end of the machining process, it is absolutely necessary to add the turning or grinding process.
The customary use of two different cutting processes to produce crankshaft pins involves considerable expenditures for machinery. To avoid these expenditures, it has already been proposed to effect the machining, particularly of crankshaft pins, by so-called rotary broaching. In this process, the workpiece is caused to rotate about the axis of the pin to be worked as in milling. The broach is then guided tangentially along the pin or pins to be worked. If a plurality of coaxial pins are to be worked on the crankshaft, all pins are worked simultaneously by separate broaches in one broach feed. With this proposed, rotary broaching, processing speeds of about 250 m/min result while conventional broaching at stationary workpieces takes place at speeds between 35 and 45 m/min, depending on the material involved.